Description of the first juvenile stage of Dilocarcinus septemdentatus (Herbst, 1783) (Crustacea, Decapoda, Trichodactylidae)

A total of 38 freshwater brachyuran species occur in Brazil, of which 79% are distributed in the northern region. However, for only two species of freshwater crabs are descriptions available for their juveniles. The importance of these studies lies in understanding oflife-cycle aspects as well the potential elucidation of phylogenetic relationships within the group because the characters are usually solely based on adult specimens. The morphology of the first juvenile stage of the Dilocarcinus septemdentatus (Herbst, 1783) is described and illustrated for the first time based on specimens hatched by an ovigerous female collected in the northeastern region of the Brazilian Amazon. Juveniles of Dilocarcinus pagei Stimpson, 1861 and D. septemdentatus have one flagellar segment on the exopod of the first maxilliped while the only described juvenile of an unidentified species of Trichodactylus Latreille, 1828 has two. Dilocarcinus septemdentatus differs from other congeneric species mainly in the number of setae on the antennae and number of segments of the mandibular palp. Variations in the number of segments and aesthetascs enable the comparison between the juveniles of D. septemdentatus with those of other Brachyuran species previously studied and suggest possible adaptations to freshwater environments.